With all due respect to the Moderator, the ORIGINAL Extra 300 was, in fact, a mid or shoulder wing design. The later 300S and 300L model had the wing located lower in the fuse.

I've flown both planes extensively and both are great choices. The decision will rests laregly on the engine you have available. For competion level vertical performance the GP kits needs a 91 two-stroke or 120 size four-stroke. The Goldberg being slightly larger/heavier requires a 120 two-stroke or 150 four-stroke.

Of the two, the GP kit is slighty more easy to tumble/snap, while the Goldberg is a little more forgiving in slow speed flight.

FWIW, the 120 size Extra 300 ARF World Models sells is a dead copy of the original Goldberg kit.